A semiconductor injection laser typically comprises a body of semiconductor material, generally Group III-V compounds or alloys of such compounds, having a thin active region between regions of opposite conductivity type, that is, i.e., a region of p-type conductivity on one side of the active region and a region of n-type conductivity on the other side of the active region. Botez, in U.S. Pat. No. 4,215,319 issued July 29, 1980 and incorporated herein by reference, has disclosed a laser, called a CDH laser, which emits a stable, single optical mode filament. The laser comprises a body of semiconductor material having a substrate with a pair of spaced substantially parallel dovetail shaped grooves in the surface of the substrate. A first confining epitaxial layer is over the surface of the substrate and the surfaces of the grooves. An active layer is over the first epitaxial layer. The active layer has a portion of uniform thickness over the portion of the surface of the substrate which is between the grooves and tapers away in thickness in either direction from the grooves. A second confining layer is over the active layer. The first and second confining layers are of opposite conductivity types. The active layer is the recombination region of the laser with the light beam being generated in the portion between the grooves. The index of refraction of the active region is greater than that of the first and second confining regions. This laser is limited, however, in its output power by the small cross-sectional area of the lasing filament.
Botez, in U.S. patent application Ser. No. 251,651, filed Apr. 6, 1981 which is a continuation-in-part of U.S. patent application Ser. No. 084,387, filed Oct. 12, 1979 and incorporated herein by reference, has disclosed a semiconductor laser, called a CDH-LOC laser, which provides a stable, single optical mode filament of light of large cross-sectional area. This injection laser comprises a CDH laser having a guide layer interposed between the first confinement layer and the active layer and which is of the same conductivity type as the first confinement layer. The guide layer is of a material having an index of refraction less than that of the active layer but larger than that of each of either the first or second confinement layers. The light beam generated in the active region then propagates both in the thin active region and the relatively thicker guide layer thereby forming a lasing filament having a significantly larger cross-sectional area. While the CDH-LOC laser disclosed by Botez produces a single optical mode filament of light of significantly greater power than that of the CDH laser, the power output in this mode is still limited.
The approach to increasing the output power in planar striped oxide lasers while retaining the coherency of the light of the output light beam has been to construct an array of closely spaced individual lasers which are phase-locked with one another so that the output of each of the lasers is coherent with that of the others and the array behaves as a single light source. Such an array has been disclosed by Scifres et al. in Applied Physics Letters 34, 259 (1979). A problem with this approach is that the close spacing between the elements of the array, which is required because of the high absorption of the light wave in the active layer and by the limited spatial extent of the optical mode in the plane of the junction in prior art planar striped oxide lasers, produces excessive electrical heating of the array when excited. This heating degrades the performance of the array. As a result, the phase-locked array can only be operated in a pulsed mode at a low duty cycle where heating is minimized. If the elements of the array are spaced far enough apart so that electrical heating of the array does not occur to the extent that it degrades the performance of the array, then the phase-locked nature of the output is lost since the elements are too far apart for optical coupling between elements to occur.